Electron beam tube



Dec. 17, 1940. J, M CAGE 2,225,330

ELECTRON BEAM TUBE Filed Apr-i1 22, 1959 Fig. l.

His Attorneg.

Patented Dec. 17, 1940 PATENT OFFICE ELECTRON BEAM TUBE John M. Cage, Schenectady, N. Y., assigner to General Electric Company, a 'corporation of New York lApplication April 22, 1939, Serial No. 269,396

9 Claims.

The present invention relates to circuits utilizing electron beam tubes and more particularly to circuits wherein a plurality of `control 'voltages applied to such atube inuence simultaneously the current ilowing therethrough.

In my Letters Patent No. 2,074,829, issued March 23, 1937 yand'assigned to the same assignee as the present application, I have described and claimed an electron beam tube wherein electronic control is accomplishedby 'deecting the beam transversely to its fpath through thev agency of a pair of deflectingv members. These deecting members are incidentally made'toserve as beam focusing means by applying lapredetermined fixed common bias tothe members.

It is an important aspect of my present invention that a secondarycontrollof the beam,` or more properly of 'the output of the-tube, may be accomplished by- Varyingl the common bias applied to the deflectingV members. Thus by-varying the beam deflectionin'accordance with a rstcontrolling inuence andvarying'the beam focus in accordance with a-second 'controlling influence, the tube outputmaybe'caused to vary as a joint function yof both of theseinuences. Furthermore,y both modes of control are accomplishedrby the useV of a common electrode structure for the deflecting members.

The novel featureswhich I believe to hecharacteristic of vmyinvention are set forth with particularity in the appended claims.- VMy invention itself, however, bothas to its organizationv and method of-operation, together with further objects and advantages thereof may bestbe understood by reference .to thefollowing description .taken in connection with the accompanying drawing,. in which Fig. 1 is .a diagrammatic view of an electron beamtube'connected in a circuit accordingto my invention andFig. Y2 shows in diagram a diiferent type of circuit in which my electron beam tube is connected in accordance with my invention.

In Fig. 1 theglass envelopel I0 contains a cathode II `which is indirectlyfheatedby a sourceof potential I2.- A focusing member. I3 partiallysurrounds the cathode I I,l and has a narrow opening I4 through which a vbeamof electrons emerges. The beam of electrons passes through la narrow opening in the accelerating electrode I5, as is explained in my LettersPatent No.2,074,829. .The cathode, focusing. member and accelerating -electrode constitute an electron gun.

After. leaving the accelerating electrode I5 the electronbeam passes Vbetween the members I6,

which form Va common means for deflectngthe (Cl. Z50-27) electron beam transversely to its path and for focusing the beam. It is then collected by either one of a pair of anodes I'I orfpasses through the opening between the anodes Il into a collecting anode I8, depending upon the amount of deflec-y 5 tion or diffusion of the beam caused by the members I6. The-anodes I'I as shown are two electrically separate members each of angle shape. They have a space remaining between them of conveniently small size through which electronsclO may pass to the collecting anode I8.

The'focusing electrode I3 is, as shown,l usually connected to the most negative terminal of a source of electromotive force'I9. The cathode II is connected to the source of potential at a pointwl5 slightly more positive `than electrode I3, and the accelerating electrode I5 is connected to a point yet more positive .than the cathode. A source of radio-frequency signals, which is represented by the primary 20 of atransformer, supplies voltagego through a tunedcircuit, comprising the secondary-2| ofV the transformer .and a 4condenser 22, across the combined electron-deflecting Vand electronsfocusing members I6. yThe signal voltages applied across the memberslinuence the elec-:I` 25 tron beam to produce corresponding deflections as the beamrv passes therebetween.

A source of high frequency energyfwhich may be represented by primary 23 of a transformer, is coupled tosecondary 24 of the transformer of...30 which one end isconnected to the central point of the secondary 2 I. The other end of the transformer secondary 24 is connected. to an intermediate point on the source of potential-I9. The connection of the common bias lead to an inter-.35 mediate point on the .potential source I9 biases both of the members I 6 .alike and produces a focusing action upon the electron beam passing between members I6. In other words,the common bias Avoltage Yvaries the mutual conductancet A of the tube to the voltage supplied froInsecondary 2I. The bias voltage necessary for proper focusing may be either positive or negative with respect tothe cathode,.depending onthe distance kbetween-thernembers I6, the voltage Vapplied to.

the various electrodes, and the structure of the tube.

superimposed upon the bias voltage developed bythe battery I9, the high frequency voltage induced in the transformer secondary 24 is also50 applied equally tothe members` I6. By this Voltage the beam focus is caused to change cyclically so that the beam density4 or cross-sectional area near the anodes II varies in accordance with the high frequency voltage supplied from the primary` 55 23. When the beam is most dense a large number of electrons can pass between the anodes I1 and be collected by the anode I8. When the beam is least dense a much smaller portion can pass between the anodes I'I, even though the beam remains undeflected and centered on the slit through the anodes I1. A large number of electrons are then collected by the anodes IT, and a small number of the anode I8.

Each anode I'I is connected to one end of a tuned circuit including a condenser 25 and a transformer primary 26. The central point of transformer primary 26 is, as shown, usually connected to the most positive point on the source I9. The anode I8 is usually connected to a point on the source I9 slightly less positive than the point to which the anodes I'I are connected. The transformer primary 26 is coupled to a secondary 2'! which is tuned by a condenser 28. This tuned circuit may supply energy to any desired consumption or output circuit.

The electron beam tube and its associated circuit as shown in this figure may conveniently be used as a converter stage in the operation of a conventional superheterodyne radio receiver. If the signal received from an antenna be impressed upon primary 2|] and a locally generated wave of fixed frequency be impressed upon the primary 23, an intermediate frequency voltage is developed across the condenser 28. The action of the members I6 upon the electron beam is such that the voltage received from the antenna deflects the electron beam and thus varies the ratio in which anodes I1 receive electrons. The voltage received from the local oscillator varies the density of the electron beam and thus varies the rate at which transfer of the electron beam from one of the anodes I'I to the other may be accomplished by the deiiecting voltage. In this way the mutual conductance of the tube to the signal voltage is controlled by the local oscillator. The voltage in the output circuit 25, 26 is therefore a voltage of intermediate frequency comprising a joint function of both the signal from the antenna and the locally generated wave. The output circuit may conveniently be tuned to the intermediate frequency which it is desired to transmit to the remainder of the superheterodyne receiver.

In Fig. 2 the same general type of electron beam tube is connected in a somewhat different type of circuit. In this figure parts previously described in connection with Fig. 1 have been given similar reference characters. Several connections to the electron gun have been omitted forthe sake of simplicity. An audio modulated high frequency voltage source represented by the transformer primary 20 is, as before, coupled to transformer secondary 2I and `supplies voltage across condenser 22 which forms a tuned circuit with the transformer secondary. This voltage is applied across members I6 so that the electron beam is deected thereby. The anodes I1 shown by Fig. 1 are replaced in this tube by a single anode 29 which has an opening in its center through which the electron beam may pass when in neutral position. The circuit is slightly modified by connection of anode I8 through transformer primary 26, which is untuned, to the most positive point of potential source I9. The anode 29 is connected to a somewhat less positive point on the source I9. Deflection of the electron beam produces a voltage variation upon anode I8 and therefore across transformer primary 26. The form of tube shown by this figure and the corresponding connections have been found more desirable for mechanical reasons than the form of tube shown by Fig. 1.

Voltage induced in the transformer secondary 21 is impressed across variable condenser 28 which forms a tuned circuit therewith and across the diode 30 and the resistor 3I. The diode 30 and its accompanying circuit operates to demodulate the wave supplied from the electron beam tube so that the modulation or audio frequency voltage derived from the carrier wave is developed across the resistor 3|, which is shunted by a radio frequency bypassing condenser 32. A suitableportion of this audio frequency voltage may be supplied to any suitable consumption device connected to terminals 33. A time delay circuit, or network, is connected in shunt with the resistor 4III and comprises a resistor 34 connected in series with a condenser 35. The cathode of the diode 30 is maintained at a fixed potential with respect to the cathode II of the electron beam tube, and theaudio frequency voltage developed across the resistor 3|, after being filtered to produce automatic volume control voltage by the time delay network, is supplied through the resistor 34 ofthe time delay network to the center of the transformer secondary 2|.

In operation the automatic volume control voltage supplied from resistor 34 biases both of the members I6 alike to vary the focusing of the electron beam. If a strong signal is received from the antenna and rectied by the diode 3U, the voltage developed across the resistor 3I varies the bias applied to the members I6 so as to reduce the focusing action of the members. When the focusing action is reduced, the gain of the electron beam tube is reduced and the signal rectified by the diode 30 is correspondingly smaller. Automatic volume control is thereby accomplished in a simple and improved manner.

It will be appreciated that the voltage applied to the various electrodes in the electron beam tube are not critical and any one or more may be varied within wide limits. The proper voltage upon theV members I6 should be determined by experiment for the desired focusing action. Other circuits and other modifications of the circuit shown which apply two distinct influences to the members I6 will occur readily to those skilled in the art. For instance, the converter system of Fig. 1 may be combined with the A. V. C. system of Fig. 2 simply by inserting the secondary of a local oscillator transformer in lead 31 of the latter figure. As another possitained byy biasing members I 6 to defocus the beam when no carrier is being received. Thus the tube itself may be used in any application Where it is desired to use some variable control voltage to vary the mutual conductance of thev tube to a signal voltage.

While I have shown particular embodiments of my invention, it will, of course, be understood bility, off-channel noise suppression may be ob-'"55 electron beam transverselyl to itspath and for varying the focus thereoLfmeans between said common means and said generating means Vfor maintaining a constant field at said generating means whereby the magnitude of saidbeam remains constant, means connected to said common means for changing the deflection ofsaid beam in response to a first varying controlling influence, and additional means connected to said common means for changing the focusof said beam in responsevto a second varying controlling influence, whereby the response of said electron receiving means is a joint function of both of said controlling inuences.

2. An electron beam tube comprising an electron gun, electron receiving means, a comb-ined electron-dellecting and electron focusing electrode structure interposed between said gun and said means, means between said structure and said electron gun for maintaining a constant field at said electron gun whereby the magnitude of said beam remains constant, a circuit connected to supply a first varying control voltage across said electrode structure for deilecting said beam transversely to its normal path, and additional means connected to said electrode structure for varying the focused condition of said beam in accordance with the variations of a second varying control voltage, and an output circuit connected to said electron receiving means whereby the tube output may be caused to vary as a joint function of said voltages.

3. An electron beam tube comprising an electron gun having an electron emitting surface for producing a beam of electrons, an anode for receiving said electrodes, a pair of combined electron-deflecting and electron-focusing electrodes positioned on opposite sides of said beam between said gun and said anode, a means interposed between said pair of electrodes and said surface and co-operating therewith to provide a controllable beam focusing system, said interposed means acting to maintain a constant field at said electron gun whereby the magnitude of said beam is maintained constant, a source of direct current for impressing a desired potential on the anode a negative terminal of which is connected to said gun, means including a first Varying voltage source for impressing different potentials on said pair of electrodes to deflect the electron beam, and controlled means for impressing a focusing voltage on said pair of electrodes and for varying such focusing voltage to vary the condition of focus of the electron beam, and means connected between said direct current source and said anode for developing an output potential which is a joint function of said delecting voltage and said focusing voltage.

4. In combination in an electron beam tube, means for generating a beam of electrons, means for receiving said electrons and impressing corresponding potential variations on an output circuit, combined electronfdeflecting and electronfocusing electrodes between said generating means and said receiving means, means interposed between said electrodes and said generating means and co-operating therewith for preventing potential changes of said electrodes from producing a changing field at said generating means, whereby the magnitude of said beam is maintained constant, means for impressing a varying voltage between said electrodes for defiecting said beam of electrons, and means for impressing a varying focusing voltage upon said electrodes and.for varying such voltage to change the con- -dition oflfocus of said beam.

- nel, a converter tube comprising an electron gun forlproducing a beam of electrons, an electron receiving member connected to said intermediate frequency channel, a pair of combined electrondeflecting and electron-focusing electrodes between said electron receiving member and said gun, means between said pair of electrodes and said electron gun for maintaining a constant field at said electron gun whereby the magnitude of said beam is maintained constant, a circuit connected between said pair of electrodes and energized by said signal receiving means, and a circuit connectedto said electrodes for impressing a variable focusing voltage on said electrodes, said focusing voltage being supplied by said .local source of oscillations, whereby the voltage impressed on said intermediate frequency channel by said electron receiving member is a joint function of the voltages of said signal receiving means and said local source of oscillations.

6. In combination with an electron beam tube comprising an electron gun for projecting a beam of electrons, electron receiving means, a pair of combined electron-deflecting and electron-focusing electrodes between said means and said gun, a circuit for impressing a modulated wave across said pair of electrodes, a circuit connected to said electron receiving means for demodulating said Waves, and a network connected to said demodulating circuit to apply a common focusing voltage to said electrodes which is a function of the magnitude of said demodulated waves.

7. In combination with an electron beam tube having an electron gun, means including a plurality of anodes for receiving an electron beam from said gun, a, pair of combined electron-deflecting and electron-focusing electrodes interposed between said gun and said means, means between said pair of electrodes and said electron gun for maintaining a constant field at said electron gun whereby the magnitude of said beam is maintained constant, a circuit for impressing an alternating voltage between said pair of combined electrodes for varying the deflection of said beam, and a circuit for impressing an alternating voltage as a variable focusing voltage between said pair of electrodes and said gun for varying the focusing action of said electrodes, whereby said first means develops a Voltage which is a joint function of said alternating voltages.

8. In an electron beam tube, means for generating a beam of electrons, means for receiving said electrons and responding to variations in said beam, a common means for delecting said electron beamtransversely to its path and for varying the focus thereof, said common means comprising a pair of juxtaposed electrodes having substantial extension along the path of said beam and adjacent thereto, means interposed between said common means and said generating means and co-operating therewith to provide a controllable beam focusing system, said interposed means acting to maintain a constant eld at said generating means whereby the magnitude of said beam is maintained constant, means connected to said common means for changing the deflection of said beam in response to a rst varying controlling influence, and additional means connected to said common means for changing the focus of said beam in response to a second varylable beam focusing system, said interposed means acting to maintain a constant eld at said generating means whereby the magnitude of said beam is maintained constant, means for impressing a varying voltage between said electrodes for deflecting said beamof electrons transversely to its path, and means for impressing a variable focusing voltage upon said electrodes and for Varying such focusing voltage to change the condition of focus of said beam.

JOHN M. CAGE. 

